Various weight selection methods and apparatus have been developed to provide adjustable resistance to exercise. For example, exercise weight stacks are well known in the art and prevalent in the exercise equipment industry. Generally speaking, a plurality of weights or plates are arranged in a vertical stack and maintained in alignment by guide members or rods. A desired amount of weight is engaged by selectively connecting a selector rod to the desired weight in the stack. The selector rod and/or the uppermost weight in the stack are/is connected to at least one force receiving member by means of a connector. The engaged weight is lifted up from the stack in response to movement of the force receiving member.
U.S. Pat. No. 4,538,805 to Parviainen discloses a weight stack machine having a stack of primary weights, and first and second supplementary weights disposed on opposite sides of the primary weights and interconnected by a bar. The combined weight of the supplementary weights is equal to the combined weight of the stack. First and second lock pin assemblies are movably mounted on respective supplemental weights for selective movement into engagement with respective sides of the top plate in the stack.
Japan Patent No. JP410118222A to Ozawa et al. discloses a weight stack machine having a stack of primary weights, and first and second stacks of secondary weights disposed on opposite sides of the primary weights. Each secondary weight appears to weigh a fraction of each primary weight. First and second selector pins are selectively inserted through desired holes in respective sides of the uppermost primary weight to selectively engage a desired number of respective secondary weights.
Exercise barbells and dumbbells are another type of weight lifting equipment that is well known in the art and prevalent in the exercise equipment industry. Generally speaking, these devices include a handle and a desired amount of weight or number of weight plates secured to opposite ends of the handle. The device is lifted up subject to gravitational force acting on the mass of the handle and attached weights. On relatively advanced devices, the bar is stored in proximity to the weight plates, and a selection mechanism is provided to connect a desired amount of weight to the bar.
U.S. Pat. No. 4,529,198 to Hettick, Jr. discloses a barbell assembly having a handle, and first and second weight boxes connected to respective, opposite ends of the handle. A base maintains first and second sets of weights in alignment with respective weight boxes. First and second flexible springs are inserted through respective boxes and through a desired number of respective weights to determine the weight to be lifted.
U.S. Pat. No. 5,779,604 to Towley, III et al. discloses a dumbbell assembly having a handle, and a plurality of interconnected opposite end weights that are stored in nested relationship to one another and the handle. One or more pins may be inserted radially or axially through the handle and a desired number of weights to determine the weight to be lifted. The dumbbell assemblies are also shown mounted on opposite sides of the top plate in a weight stack.
Despite the foregoing advances and others in the field of weight selection, room for improvement remains.